1. Field of the Invention
The present invention relates to a microwave oven, and more particularly, to a control method for such a microwave oven, in particular, a microwave oven having a popcorn cooking mode to cook popcorn.
2. Description of the Related Art
Generally, microwave ovens are adapted to irradiate microwaves of 2,450 MHz onto food to be cooked, thereby cooking the food. The microwaves vibrate molecules of the food which are, in turn, struck against one another, thereby generating heat. By this heat, the food is cooked. FIG. 1 illustrates a general microwave oven. As illustrated in FIG. 1, the microwave oven includes an oven body 102, and a door 104 hingably mounted to the oven body 102 to open and dose a cooking chamber 106 defined in the oven body 102. A tray 110 is placed on the bottom surface 108 of the cooking chamber 106 within the cooking chamber 106. The tray 110 rotates during a cooking operation so that microwaves are uniformly transmitted to the entire portion of the food. A display unit 112 is provided at the front surface of the oven body 102 in order to display cooking time and other set values. A manipulation panel 114 is also provided, which has manipulation keys 116 to select a desired cooking mode, a desired cooking time, etc. When the user desires to cook food, the user manipulates the manipulation keys 116 to set a desired cooking condition in a state in which the food is placed on the tray 110, and then presses a cooking start key. In response to the start key, microwaves are transmitted to the food in a state in which the tray 110 rotates. Thus, the food is cooked.
Using such a microwave oven, various kinds of food can be cooked. For example, popcorn is a representative food capable of being cooked using a microwave oven. Popcorn products for microwave ovens are commercially available. In such a popcorn product, corn grains, that is, the raw material of popcorn, are contained in a paper bag in a sealed state. Cooking of such a popcorn product is carried out in a state in which the popcorn bag is placed in the microwave oven as it is. During the cooking operation, the corn grains contained in the sealed bag are popped as moisture escapes therefrom. That is, the moisture of corn grains is vaporized, so that the corn grains abruptly increase in volume, thereby forming popcorn. The popcorn has greatly increased volume as compared to the initial corn grains. Taking into consideration this fact, the popcorn bag should have a sufficiently large size.
FIG. 2 illustrates the alterations in the shape and size of a popcorn bag exhibited during a cooking operation carried out for corn grains contained in the popcorn bag using a microwave oven in accordance with a conventional control method. Referring to the part I of FIG. 2, a commercially-available popcorn product for microwave ovens is illustrated in which corn grains are contained in the central portion of a popcorn bag with opposite side portions being folded to overlap with each other. Accordingly, the commercially-available popcorn product illustrated in part I has a small size corresponding to only about ⅓ of the size of the popcorn bag in a popped state.
As the popcorn product is cooked, it size and shape are gradually changed, as illustrated in respective parts of FIG. 2. That is, as heating proceeds from an initial state shown in part I of FIG. 2, the folded portions of the popcorn bag are gradually unfolded, as illustrated in part II of FIG. 2. Subsequently, the popcorn bag becomes completely unfolded, as illustrated in part III of FIG. 2. As the heating operation is continued, the corn grains contained in the popcorn bag are popped, thereby causing their volume to increase gradually. As a result, the volume of the popcorn bag is also increased. At this time, however, the popcorn bag is reduced in length due to the volume increase thereof.
Although the content of the popcorn product may vary somewhat among different manufacturers, there are mainly two representative contents. In the United States of America, the home of popcorn, popcorn products with the largest content of 3.5 oz. are most popularly sold. In Korea, these popcorn products having the content of 3.5 oz. are most commonly imported and sold. Where the bottom area of the cooking chamber is smaller than that of the popcorn bag with the above mentioned large content, a problem occurs during a cooking operation. This will be described with reference to FIG. 3.
FIG. 3 is a view illustrating the state of the interior of the microwave oven during an operation to cook a popcorn product with a large content in accordance with the conventional control method. As a cooking operation is carried out under the condition in which the tray 110 rotates, the popcorn bag is completely unfolded to achieve its maximum length, as illustrated in part I of FIG. 3. Where the maximum length of the popcorn bag, that is, the length of the popcorn bag in the completely unfolded state, is longer than the shorter-side length of the bottom 108 of the microwave oven, the popcorn bag come into contact with the inner wall surface of the cooking chamber 106 at its corners, so that it no longer rotates even though the tray 110 rotates continuously. As a result, the popcorn bag is moved from the central portion of the cooking chamber 106 toward one corner of the cooking chamber 106, and finally stays at that corner.
For this reason, microwaves are non-uniformly transmitted to the popcorn bag. That is, there is a problem in that microwaves are insufficiently transmitted to the portion of the popcorn bag positioned adjacent to the corner of the cooking chamber 106.